This present invention relates general to tool joints and more particularly to an externally visible indicator for facing the tool joints of drill pipe and other tubulars.
As described in U.S. Pat. No. 4,438,953 to Timme, Jr., a string of oil and gas well drill pipe is made up of sections of pipe, each about 30 feet long. Each section has an externally threaded pin on one end and an internally threaded box on the other end. When coupled together, the pin and the box form a tool joint. Each set of threads is tapered and has a point where the pitch diameter is a specific amount, this point being known as the gage point. A make-up shoulder is spaced a selected distance from the gage point of the threads on the pin. Another make-up shoulder is located at the outer end of the box. When fully made-up, these make-up shoulders contact each other under a selected amount of compression to provide a fluid-tight seal. To achieve the proper amount of compression, the distance from the pin make-up shoulder to the gage point of the pin threads, and the distance from the box make-up shoulder to the gage point of the box threads, must be carefully controlled.
During use, the make-up shoulders may gall and score. To achieve a smooth surface again, the shoulders are redressed. It is important that the total material removed from the two mating shoulders be no more than {fraction (1/16)} inch from original, or no more than {fraction (1/32)} inch from any shoulder. If the material removal totals more than {fraction (1/16)} inch from mating shoulders, inadequate compression may occur during make-up, thus requiring the mating faces to be remachined. Without such corrective measures, fatigue failures and washouts may result.
The American Petroleum Institute recommends to manufacturers the use of an indented circle and tangent bar or line stamped into the tool joint pin and the box counterbore. The bar would be impressed into the metal exactly ⅛ inch from, and parallel to, the make-up shoulder. This method has two shortcomings. First, it must be hand-applied. Therefore, it is time consuming and potentially unreliable. Also, this method marks only one point of the pin or box.
In the '953 patent, Timme, Jr. taught a bench mark consisting of a bench mark shoulder formed around the pin outer diameter ⅛ inch from the make-up shoulder. The box counterbore had a step formed around it ⅛ inch from the make-up shoulder. The bench mark shoulder provided a reference line to determine the distance from the makeup shoulder to the reference line, after the make-up shoulder had been redressed. Because the bench mark was a continuous step around the circumference of the pin outer diameter, and a continuous counterbore around the circumference of the box inner diameter, it also served as an indicator of uneven machining of the tool joint shoulder. The mark was placed on the tool joint during the operation in which threads were machined onto the tool joint.
The benchmark shown and described in the '953 has proven to be successful, but suffers from a drawback in that, when the joint has been made up, the benchmark can neither be seen nor measured. In order to determine if the maximum amount of facing has been performed on the mating shoulder surfaces, the joint must be uncoupled, and a measurement made to make this determination. Also, certain prior art benchmarks require the removal of a thread protector, and a certain amount of cleaning of the connection itself prior to making a determination as to whether or not the faces must be machined.
Thus, there remains a need for a externally visible and measurable refacing indicator for a tool joint. Such an indicator should be easily manufactured, and not increase the cost of the pin or the box elements which make up the tool joint. The present invention is directed to this need in the art.